Static eliminator device



2 Sheets-Sheet 1 Sept. 29, 1970 R. A. JACKSON I STATIC ELIMINATOR DEVICE Filed Feb. 8, 1968 I N VE N TOR. fi/c/mkmqJqz-xran BY W J M flrraRM-XS.

Filed Feb. 8, 1968 I \ie wkkfimm mu 2 Sheets-Sheet 2 QB RSkhm MR3 t zuk w w w wh United States Patent C US. Cl. 317-2 2 Claims ABSTRACT OF THE DISCLOSURE A device for eliminating the static charge from moving webs or the like which advantageously utilizes the characteristics of two basic types of static eliminators, i.e. an electrically or radioactivity energized static eliminator having selected relatively limited capacity and a non-energized induction static eliminator in combination. The combination device exhibits a substantially higher ionization current capability than either of the components, which is to an extent self-adjusting. Initially the induction component acts on the web reducing the web potential to a value which does not exceed the threshold potential of the induction component. Next, as the web passes the energized component, the web potential is further reduced to a desired level.

This invention relates to an apparatus for eliminating static charge from moving webs such as, for example, those used in plastic or paper coating, bagging, or laminating operations.

It is well known that in various operations where sheet material moved in frictional engagement with guide rolls, guide bars and the like, undesirable static electric charges develop. This phenomenon becomes particularly objectionable in machines of the kind operating on a continuous moving web and under conditions where the humidity is relatively low, as in the winter. The frictional engagement between the web and a dilferent material causes the creation of static electrical charges on the surface of the Web which may accumulate to high levels. This situation is a definite safety hazard to workers as it may serve as the source of ignition of flammable solvents. Further, it is the cause of dust accumulation on non-conductive surfaces and impedes the processing of light weight films and fibers.

In order to obviate this difficulty and keep the Web at some desired electrical condition, as at ground potential, various forms of static eliminators have been developed.

Generally presently known static eliminatorsmay be categorized in two classes, namely, induction type static eliminators and energized static eliminators. Induction, or non-powered, units generally consist of either grounded needles or metallic brushes suspended above the web surface to be neutralized.

Induction units are effective only if the web potential is sufficiently high to ionize the atmosphere between the needle points and the Web, to allow neutralization of the charge on the web surface. Thus, the induction device is effective only at relatively high web potentials. For example, at web potentials below about 5 to kilovolts an Patented Sept. 29, 1970 induction static eliminator will not ordinarily function to provide the necessary ionization to neutralize the static charge.

Energized static eliminators may be further categorized as to what source of energy is applied to ionize the air. Electrically powered units are generally similar in construction to the induction static eliminators wherein the needles are connected either directly or capacitively to a high voltage AC power supply which causes ionization in the air gap between the needle points and a proximity ground. This voltage can range from 5,000 to 15,000 volts and even higher. Electrically powered units are generally effective to dissipate the static charge from webs with low potentials which are of themselves not sufficient to effect the necessary ionization by an induction static eliminator between the web and the needles. Thus, powered static eliminators may be effective where induction units are not, due to low web potentials. However, the pos- Sibility of ignition of solvents in the event of electrical breakdown of powered static eliminators often precludes their use in flammable atmospheres. Further, there is a definite shock hazard.

Radioactively energized static eliminators, i.e. those in which ionization of air is effected by the interaction of alpha, beta, or gamma radiation, are also effective at low web potentials where the non-energized (induction) units are not. The maximum ionization current produced by a nuclear static eliminator depends on the amount of radioactivity which the device contains and decreases as the radioactivity decreases with the half life of the radioisotope employed. Obviously, if only a nuclear unit is to be employed to neutralize low web potentials, the amount of radiation required to effect ionization will crease substantial problems of safety as well as cost.

It is an object of the present invention, therefore, to overcome the static charge build-up problems discussed above through the provision of an eifective and relatively inexpensive static eliminating device which utilizes the desirable characteristics of both induction static eliminators and energized eliminators. Other objects and advantages inherent in the invention will become apparent from the following detailed but non-limiting description.

In accomplishing the noted objects, the invention provides a device comprised generally of a first component which has a limited ionization-current capability (i.e. a nuclear or electrically powered component) which operates at low web potentials and a second component which responds to the web potential (i.e. an inductionstatic-eliminator). The combination device of the invention thus provides a substantially higher ionization current capability than either component could provide separately. The apparatus is both safe and highly effective.

The apparatus of the invention for eliminating static charge from a moving web or the like comprises in combination an induction means including a plurality of elongated, parallelly-extending, electrically conductive and grounded members adapted to be positioned at a predetermined distance from said web for effecting an ionization of the atmosphere between the surface of the Web and said members when the static charge therebetween exceeds the ionization potential of said atmosphere so as to neutralize a portion of said static charge as the web moves relative to said members at said predetermined distance, and an elongated, electrically conductive, energized means positioned at a spaced distance from and in close proximity to the end points of the grounded members of said induction means to act upon the portion of the web which has passed by said induction means so as to effect an ionization of the atmosphere between the surface of the web and said conductive means for neutralizing the static charge from said web remaining after the web has passed by said induction means, the spaced distance being at least equal to the length of said elongated members of the induction means.

Further details of the invention will now be described with particular reference to the accompanying drawings exemplifying the best means presently comtemplated for carrying out the invention, wherein:

FIG. 1 is a perspective schematic view in partial crosssection of a combination induction and radioactively energized static eliminator for moving webs;

FIG. 2 is a diagrammatic sketch of another embodiment of the invention wherein the energized component thereof is comprised of an electrically powered static eliminator;

FIG. 3 is a graph showing the individual and combined effectiveness of a combination of radioisotope energized and inductive static eliminators; and

FIG. 4 is a similar graph showing the individual and combined effectiveness of low-capacity electrically powered and inductive units.

Referring now in detail to the accompanying drawings, FIG. 1 illustrates a static elimination device 10 for a moving web 12, whose direction of movement is indicated by the arrow, which comprises basically two components in combination, namely, a first elongated induction component 14 including a plurality of elongated, parallellyextending, electrically conductive and grounded members 16 (e.g. wire needles) held in electrically conductive support 17 adapted to be positioned at a predetermined distance 18 from the surface of the moving web and a second, elongated, electrically conductive, radioactivity energized component 20 positioned at a spaced distance from, and in close proximity to, the elongated members 16 (needles) of the induction component to act upon the portion of the web 12 which has passed by and has been acted upon by the induction component. The spaced distance which separates the radioactivity energized component 20 from the end points of the elongated members 16 (needles) of the induction component must be at least equal to the length of the elongated members (needles) of the induction component. The needles shown are constructed with a coiled, spring-like shank so that they can be deflected if contacted by a moving object. The induction component 14 and the radioactivity energized component 20 are integrally connected by means of a common mounting member 22. A nonconductive shield 24 (eg of plastic) is optionally mounted on the induction component parallel to and extending along and beyond the length of the elogated members 16 to protect said members from coming into contact with the web.

The radioactivel energized component 20 is comprised basically of U-shaped elongated metal member housing a radioactive source 26, preferably in the form of a compact monolayer of a multitude of discrete microspheroidal particles (not shown) containing e.g. about 18 millicuries of polonium per foot of length. The energy-emitting face 28 of the radioactively energized component is provided with a metal screen member 30 to prevent damage to the radioactive source while allowing radiation to pass through freely.

Other radioactive materials can be used, such as americium krypton (contained in a tube), promethium and the like.

FIG. 2 illustrates diagrammatically another embodiment of the invention, wherein the energized component includes a bar 32 which is substantially similar to the induction component 14 but wherein the elongated needle members 34 thereof are connected either directly or capacitively to a high voltage power supply 36. Said energized component is provided with a proximity ground 38 which is electrically connected to the induction component 14.

In typical specific embodiments both components will extend practically across the entire width of the web and will be positioned above the We l) or other workpiece in accordance with the particular conditions encountered. In specific instances it will be necessary to so position the device, and to provide such energization of the energized means, as to accomplish the required neutralization of the charge. The actual values will depend on web speed and the web potential and capacitance of the system.

The effect of the above combination device is that as the web moves past the needles of the induction component, a portion of the static charge on the web surface is neutralized when the web potential between the needle points and the web surface exceeds the ionization potential of the atmosphere therebetween. Next, as that portion of the web which has been acted upon by the induction component passes 'by the energized component, the residual static charge is neutralized by the energized component.

Thus, in operation, the maximum residual web potential, after passing by the induction component, is the threshold potential for the energized component. The energized component then requires only sufficient ionization current to reduce this residual potential to a desired level. This reduces the radioactivity requirement (in the case of a nuclear component) or the ionization current requirement (in the case of an electrically powered component) required to reduce this residual potential to a desired level.

Because of the constant fluctuation in the quantity of static electricity generated due to variations in such variables as humidity, the nature of the material being processed, and web speeds, it is desirable to provide a device which responds to changes in the amount of charge.

The apparatus of the invention is responsive to fluctuations in charge. The induction component becomes more effective as the level of charge and the web potential increase and is a self-adjusting part of the combination, maintaining the Web potential at a level equal to or less than the threshold potential of the induction component (said threshold potential being equal to the web potential at which the induction component begins to neutralize the charge). The concomitant operation of the energized component insures that the residual web potential will be reduced to the desired level.

What is claimed:

1. Apparatus for eliminating static charge from a moving web or the like comprising in combination:

an induction means including a plurality of elongated. parallelly extending, electrically conductive and grounded members having endpoints adapted to be positioned at a predetermined distance from said web for effecting an ionization of the atmosphere between the surface of the web and said members when the static charge therebetween exceeds the ionization potential of said atmosphere so as to neutralize a portion of said static charge as the web moves relative to said members at said predetermined distance,

a U-shaped elongated member housing a radioactive source adapted to emit alpha radiation from the Open end of said U-shaped elongated member in a direction substantially perpendicular to and toward said web,

said U-shaped member positioned in close proximity to said endpoints of the elongated members of said induction means, but not closer than a distance equal to the length of said elongated members, to act upon that portion of the web which has passed by said in duction means so as to eflect an ionization of the atmosphere between the surface of the web and said radioactive source, said radioactive source comprising polonium in the form of a compact monolayer of a multitude of discrete microspheroidal particles. 5 2. The apparatus in accordance with claim 1 wherein said U-shaped elongated member is positioned in close proximity to the endpoints of the elongated members of said induction means at a distance about equal to the length of said elongated members.

References Cited UNITED STATES PATENTS 1,243,262 10/1917 Coberly 317-2 2,479,882 8/1949 Wallhausen et al. 0106 2,048,490 7/1936 Bilstein 3172 6 1,735,494 11/ 1929 Chapman 317-2 2,264,683 12/ 1941 Smith 178*48 2,333,213 11/1943 Slayter 3172 3,264,473 8/ 1966 Levin et a1 250-44 3,396,917 8/1968 Carter 242 FOREIGN PATENTS 954,185 12/1956 Germany. 886,180 8/ 1953 Germany.

OTHER REFERENCES The Inland Printer, vol. 121, No. 2, May 1948, p. 60, entitled Static Eliminator.

J. D. MILLER, Primary Examiner C. L. YATES, Assistant Examiner 

